How would I draw, in Tikz, the following diagram of the behaviour of gamma rays under the influence of a magnetic field?

Question

Answer 1

Third version. I tried to make cleaner code. The only problem is for the magnets with rounded corners. My method is this case is not correct. The work with plans is interesting but it's preferable to draw the magnets in 2D, it's for easy to fill the magnets. The "front" faces and "back" faces are easy to draw with rounded corners but the lateral surface is very boring. I's certainly possible to improve the next code.

\documentclass[]{scrartcl}
\usepackage{tikz}
\usetikzlibrary{arrows,3d,calc,intersections}
\begin{document}

\begin{tikzpicture}[x  = {(-0.65cm,-0.45cm)},
                    y  = {(0.65cm,-0.45cm)},
                    z  = {(0cm,0.8cm)},
                    scale = 2,
                    color = {lightgray}] 

% style of faces
\tikzset{facestyle/.style={shade,line join=round,
                           bottom color=darkgray!60,
                           top color=lightgray}}

\path (1.5,1.5,2) coordinate (c);  
\path[facestyle] (0,0,2) -- (0,2,2) --(2,2,2)--(2,0,2)--cycle ; 
% face "left"
\begin{scope}[canvas is zy plane at x=2]
  \path[facestyle] (0,0) rectangle (2,2);
  \path (0.2,2) 
    coordinate (f1) -- (0.2,1.4)
    coordinate (f2) -- (1,1)
    coordinate (f3) -- (2,1) 
    coordinate (f4) -- (c)--(2,2) 
    coordinate (f6);
\end{scope} 

% face  "right"
\begin{scope}[canvas is zx plane at y=2]
  \path[facestyle] (0,0) rectangle (2,2);
  \path (0.2,2) 
     coordinate (g1) -- (0.2,1.4) 
     coordinate (g2) -- (1,1)
     coordinate (g3) -- (2,1)
     coordinate (g4) -- (c) -- (2,2)
     coordinate (g6);  
\end{scope}    
%<------------------    other faces ------------------------------> 
% face "front or left" magnet 2
\begin{scope}[canvas is zy plane at x=-5]
  \path[facestyle] (-0.05,-4.5) rectangle (1.95,-2.5);  
\end{scope}  
% face arriere magnet 1
 \begin{scope}[canvas is zx plane at y=0]
   \path[facestyle] (5,4) rectangle (7,7);  
   \draw[black] (6.98, -0.5) -- (6.98, 4);     
\end{scope}  
% face front magnet 1
\begin{scope}[canvas is zy plane at x=3]
  \path[facestyle] (2.5,-4) rectangle (0.5,-2);  
\end{scope}
% face sup magnet 1  
\begin{scope}
 \draw[facestyle]
       (1,-3,3.60) --  (1,-1,3.60) --  (4,-1,3.60) -- (4,-3,3.60);
 \draw[facestyle]  
       (-3.5,-3,3.60) --  (-3.5,-1,3.60) --  (-7,-1,3.60) -- (-7,-3,3.60) ; 
\end{scope}

%<------------------ cutout  ------------------------------>  
\draw[shade,color=gray,double=lightgray,double distance=1pt]%
   (f4) to [in=230,out=-15] 
   (c)  to [in=180 ,out = 80]
   (g4) to [in=20,out=190]
   (g3) to [in=30,out=190]
   (g2) to 
   (g1) to 
   (f2) to [in=20,out=100]
   (f3) to [in=-160,out=-120]
   (f4)
    ;
%<-------------------  hole in the box  ------------------------------> 
\fill[double=lightgray,double distance=1pt,top color=black!80,shade]%
              (0,0,.8) circle [x radius=2mm,y radius=1mm, rotate=15];
%<-------------------  source of rays --------------------------------> 
\fill[black!80] (1,1,0) circle [x radius=2mm,y radius=1mm, rotate=15];
%<-------------------  rays Gamma  ---------------------------------->
\begin{scope}[black!60,>=open triangle 45,line width =2]
 %  ray
 \draw (.7,.8,0)--++(0,0,1);    
  \draw[->] ((.7,.8,1.85)--++(0,0,7) ;      
 %  ray  
 \draw (.8,.7,0)--++(0,0,1);    
 \draw[->] (.8,.7,1.85)--++(0,0,8) ; 
 %  ray         
 \draw (1,1,0)--++(0,0,1.4);   
 \draw[->] (1,1,1.85)--++(0,0,9) node [above]{Gamma};  
\end{scope}


%<------------------- end rays Gamma  ------------------------------>


%<-------------------  rays Beta  ---------------------------------->

\begin{scope}[canvas is xz plane at y=1,black!60,>=open triangle 45,
             line width =2,rounded corners]
%  ray
\draw (1.1,0) -- ++(0,1.4);    
\draw[->,] (1.1,1.95) -- (1.1,6) -- (3,11) ; 

%  ray
\draw (1.2,0) -- ++(0,1.4);     
\draw[->] (1.2,1.95) -- (1.2,6) -- (4,10);
%  ray
\draw (1.15,0) -- ++(0,1.4);     
\draw[->] (1.15,1.95) -- (1.15,6) -- (3.5,10.5)node [above]{Beta};   

%<------------------- End  rays Beta  ------------------------------>    

%<-------------------  rays Alpha  ------------------------------>    
\draw (0.9,0) -- ++(0,1.5)
      (0.9,1.8) -- (0.9,6) to (-.5,5.8) coordinate (d);   
\draw[->,lightgray] (d) -- (-3,5.5) coordinate (d) ;

\draw (0.8,0) -- ++(0,1.45)
      (0.8,1.8) -- (0.8,5.7) to (-.5,5.6) ;   
\draw[->,lightgray] (-.5,5.6) -- (-3,5.3); 

\draw (0.85,0) -- ++(0,1.45)     
      (0.85,1.8) -- (0.85,5.5) to (-.5,5.4) ;
\draw[->,lightgray] (-.5,5.4) -- (-2.5,5.2);  
\end{scope}

%<--------------------------- face right  magnet 2 --------------------> 
\begin{scope}[canvas is zx plane at y=2]
  \path[facestyle,opacity=.8] (5,-4) rectangle (7,-0.5); 
\end{scope}  
%<---------------------------rays of magnets  ------------------------>
\begin{scope}[canvas is zx plane at y=2]
  \path[facestyle] (5,4) rectangle (7,7);
  \draw[black] (7,  -0.5) -- (7,  4)
               (5,  -0.5) -- (5,  4)
               (6,  -0.5) -- (6,  4)
               (5.5,-0.5) -- (5.5,4)
               (6.5,-0.5) -- (6.5,4) 
               (7.45,-.05)-- (7.45,4.45)
               (7.9,.35)  -- (7.9,4.85)
               (8.35,0.75) node[above right=1cm]{\textcolor{black!50}{NORTH}}%
            -- (8.35,5.25) node[below left=1cm]{\textcolor{black!50}{SOUTH}}
               (8.8,1.15) -- (8.8,5.65); 
 \end{scope}
  \node[black,right] at (d)  {Alpha};
 \end{tikzpicture}   
\end{document}

I try magnets with rounded corners but the result is not pretty and there are a lot of approximations

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